In Greek mythology, Erebus, or Erebos was a primordial god, personification of darkness, offspring of Chaos alone. He was brother of Nyx and father of Aether by himself and, with Nyx, Hemera, Moros, Charon, Eros and the Keres. According to some later legends, Erebus was part of Hades, the underworld. It was where the dead had to pass immediately after dying. After Charon ferried them across the river Acheron, they entered Tartarus, the underworld proper. Erebus was often used as a synonym for Hades, the Greek god of the underworld. Also, Erebus was the name of the gloomy space through which souls passed on their way to Hades. In pre-Homeric mythology, he formed an incestuous liaison with his mother to create the first elements of the cosmos, Aether (light) and Hemera (day).